Originally Posted by deepor
I think that's normal, each individual fan is slightly different. Maybe also every motherboard fan header is different? And I know if I put two fans onto a Y-cable, then I get lower speed on the one fan that I can measure through the Y-cable.
I only have good measurements for two Silent Wings 3 High Speed PWM. Here's two CSV files with my measurements:
All of these measurements were done on the exact same motherboard fan header. The fans were mounted with open air in front and behind them. The fans were in the front of the case, the side panel was open, the front panel was removed, there was no dust filter, there was no drive cages or similar behind the fans.
Interesting results. I wasn't to terribly surprised to see differences between samples of my sub $7/each fans, but I'd be pretty irritated if I had spent $20++ per fan and still had that kind of inconsistency.
The Y-splitter results don't surprise me, especially since it starts to trail off at higher speeds. The additional power draw of the second fan probably causes a bit more voltage drop.
I just went through testing my 6 front radiator fans and I'm pretty confident that there was a revision of some sort. I left the fans on the radiator, but tested one at a time. My "free air" test results show a similar trend overall, and being "on the rad" doesn't seem to affect speed until above 50%. Anyway, I had 3 new fans on the push side of the rad, and 3 old fans on the pull side. The 3 new fans all behaved similarly, and the 3 old fans were similar as well, but I averaged the 3 samples for each. New vs old however, is not so close:
PWM "NEW" P14 "OLD" P14 OLD - NEW
20% 388 254 -134
30% 556 454 -102
40% 722 650 -72
50% 872 826 -46
60% 1015 984 -31
70% 1156 1141 -15
80% 1285 1290 4
90% 1410 1427 16
99% 1565 1601 36
The low end of the "old" fans is slower, around 250-260 RPM at 20% (even in free air), while the "new" fans all run around 370-390 RPM at 20%. Even in free air, there's a distinct crossover point at around 75% where the "old" fans start running slightly higher speeds than the new ones.
I find 1000 RPM to be about the absolute limit I can tolerate noise wise, so I went ahead and swapped the old fans out for new ones so that all 6 of my front rad fans run close in speed off the same Splitty9. Whether or not it makes a difference, who knows. But it makes me feel better at least.